1. Field of the Invention
This invention relates to a tape cassette and more particularly to a tape cassette which is not dislocated nor slipped out of the cassette body even when impact is applied to a slider mounted on a cassette body for forward and backward movement.
2. Description of the Prior Art
A conventional tape cassette will be described with reference to FIGS. 3 through 7. This conventional tape cassette, as shown in FIG. 3, comprises an upper half 1 and a lower half 2 constituting a cassette body which rotatably contains a hub (not shown) with a tape wound thereon, a slider 3 disposed in such a manner as to cover the lower half 2 for movement forward and backward, and a spring (not shown) disposed to a front end of the lower half 2 in order to normally urge the slider 3 forward, a front cover 4 being disposed to front edges of the upper and lower halves 1 and 2 in such a manner as to be able to open and close, so that the front edges are opened or closed depending on whether the cassette tape is being used or not.
The lower half 2, as shown in FIGS. 4 through 6, are integrally provided with a pair of retaining elements 22 each having a projection 22A at a free end thereof, the projection 22A being able to engage in a first or second hole 32, 33, the first hole 32 being formed in a front part of the slider 3 and the second hole 33 being formed in a rear part thereof. In accordance with the reciprocal movement of the slider 3, the projections 22A of the retaining elements 22 are moved upward and downward relative to a surface of the lower half 2 and engaged in the first or second hole 32 or 33 so that the retaining elements 22 are retained in positions for opening and closing a pair of opening portions 21, 21 formed in the lower half 2 through a pair of opening portions 31, 31 formed in the slider 3.
Each of the retaining elements 22, as shown in FIG. 4, is formed into an elongated rectangular form extending in the forward and backward direction from its one end (or one side) integrally connected to the lower half 2, and a gap 23 is formed between the remaining three sides of the retaining element 22 and the lower half 2.
In the conventional tape cassette, the projection 22A of each of the retaining element 22 integrally connected to the lower half 2 is symmetrically formed when viewed in cross section in the longitudinal direction of the retaining element 22 as shown in FIGS. 6 and 7. That is, the height l.sub.1 of a perpendicular surface 221A of the projection 22A on the connecting side of retaining element 22 and the height l.sub.2 of a perpendicular surface 222A of the projection 22A on the tip side (or free end) side of the retaining element 22 are formed into the same dimension l.sub.1 =l.sub.2), so that the perpendicular surface 221A normally receives a biasing force P owing to the spring through the first hole 32 of the slider 3 or the second hole 33 thereof. If the height of the projection 22A is represented by l.sub.3, it is usually such that l.sub.3 /l.sub.1 =1.2.about.1.7.
Furthermore, both the perpendicular surfaces 221A and 222A have guide surfaces 223A and 224A inclined inwardly and upwardly respectively so that the retaining elements 22 are guided inwardly through these guide surfaces 223A and 224A when the slider 3 is reciprocally moved.
When the conventional tape cassette is loaded in a recording/reproducing apparatus at the time the tape cassette is used, the front cover 4 of the tape cassette is opened and the slider 3 is moved backward against the biasing force P of the spring. As a result, the opening portions 31, 31 of the slider 3 are overlapped with the opening portions 21, 21 of the lower half 2. As a result, a driving portion of the recording/reproducing apparatus is brought into engagement with the hub so that the hub will be ready to rotate. At that time, the retaining element 22 of the lower half 2 is engaged in the first hole 32 of the slider 3 by its projection 22A to retain the slider 3 in order to maintain the first hole 32 in its open state as shown in FIG. 6.
On the other hand, when recording to or reproducing from the tape is over and the tape cassette is removed from the recording/reproducing apparatus, the retaining element 22 of the lower half 2 is pivoted about the connecting portion when the slider 3 is moved forward by the biasing force P of the spring. As a result, the projection 22A is disengaged from the first hole 32 of the slider 3 and pushed into the lower half 2 to climb over a plane between the first hole 32 and the second hole 33 into the second hole 33, and the opening portion 31 of the slider 3 slider from the opening portion 21 of the lower half 2. Since the opening portion 31 and the opening portion 21 no longer overlaps, the opening portion 21 of the lower half 2 is closed.
However, since the upper and lower halves 1 and 2, the slider 3, etc. of the tape cassette are formed, in general, by injection molding from synthetic resin, they are easily deformed under a high atmospheric temperature. Also, since the retaining element 22 receives the biasing force P of the spring by the perpendicular surface 221A of the projection 22A on the connecting side of the retaining element 22 through the slider 3, the retaining element 22 has a tendency to bend inwardly owing to the moment of rotation of the biasing force P. Moreover, in the conventional tape cassette, when the projection 22A is bent, even by a small amount, by the moment of rotation received by the retaining element 22 from the slider 3, the engaging state between the projection 22A and the first hole 32 or second hole 33 of the slider 3 becomes insufficient. When impact is applied to the tape cassette in the foregoing state, the retaining function of the retaining element 22 is canceled, and there is a danger that the slider 3 will move forward excessively, owing to the biasing force P of the spring and will be slipped out of the lower half 2.
On the other hand, there remains the problem that, since the heights l.sub.1, l.sub.2 of both the perpendicular surfaces 221A, 222A of the projection 22A are set such that the slider 2 is retained in its opened or closed position and the projection 22A is disengaged from the hole 32 or 33 at the moment the slider is reciprocally moved, the heights are naturally limited.